The present invention relates to an improved configuration for connecting the needle drive and stroke adjustment to the main shaft of a tufting machine, and more particularly a "dial type" adjusting mechanism tufting machine.
In dial type adjusting mechanism tufting machines, adjustment of the stroke of the tufting machine is usually made by changing the point of attachment of an eccentric rod to a drive lever through which an oscillating motion from an eccentric cam mounted on a rotating driveshaft is applied to a rocker-type or oscillating shaft, the needles being reciprocally driven by push rods connected to the rocker shaft. Mechanisms of this type are well known in the art, examples being illustrated in U.S. Pat. Nos. 2,977,905 and 3,881,432. FIGS. 6 and 7 U.S. Pat. No. 2,977,905 are reproduced in the accompanying FIGS. 1 and 2 for comparison purposes. Needle stroke changes are performed at each end of a dial type machine and are usually accomplished by moving the point of attachment from an eccentric rod to a drive lever, the drive lever having an arcuate slot with a center curvature coinciding with the geometric center of the eccentric cam when the cam is at bottom dead center.
Several inherent disadvantages have been encountered in previous dial type adjusting mechanisms. The first problem concerns the nonuniform nature of the forces applied to the needle mechanism arising from the changes in leverage of the slotted drive lever upon adjustment. A second problem related to the nonuniform nature of the forces is the increased vibration at high speeds where the drive lever and needle mechanism are raised and lowered in unison rather than in opposition to one another. A third problem is that the slotted drive lever or its connection with the eccentric rod can be structurally intolerant of the forces transmitted by high speed tufting machines. A fourth problem is crowding at the ends of the driveshaft, a position that usually serves as the drive mechanism not only for the needle drive, but also for the backing feed drive, the yarn feed drive, the knife rocker shaft, the looper rocker shaft or jack shaft, and one or more optional attachments. A fifth problem is that the driveshaft has heretofore been mounted proximate to the side or bottom of the machine head, making it difficult or impossible to use counterweights to reduce the vibrations which occur at high speeds.
As a result of the above-mentioned disadvantages, it has proven difficult to manufacture a dial type tufting machine which would operate reliably without excessive vibration at speeds in excess of 800 revolutions per minute. Because the dial type tufting machines are less expensive to manufacture and maintain than the high speed machines of the type illustrated in U.S. Pat. Nos. 3,839,972; 3,857,345; and 4,515,096, considerable effort has been devoted to improving the performance of the dial type machines. Examples of such improvements include the use of an adjustable eccentric drive and eccentric rod connecting to an unslotted drive lever in the place of the drive lever with an arcuate slot to adjust the needle stroke as claimed in U.S. Pat. No. 4,834,005, as well as the use of individual needlebar drive assemblies with demountable stroke cams and connecting rods as claimed in U.S. Pat. No. 4,665,845.
In all dial type machines heretofore manufactured, the driveshaft has been located substantially below the rocker shaft. This relationship is inverted in the present invention, which leads to a substantial increase in the operating speed of the tufting machine.